Co-owned U.S. patent application Ser. No. 14/797,348, filed on Jul. 13, 2015, details certain techniques for characterizing bubble sizes as well as contact angles between bubbles and particles in real-time from images taken within a froth flotation system, and that application is fully incorporated herein by reference.
It is known to induce bubbling into a solution so as to float particles to the surface for recovery or recycling of such particles. The particles may be valuable to be recovered for example where the solution is mining effluent, or they may be pollutants to be disposed of for example where the solution is an industrial waste stream from a recycled paper re-processing facility. FIG. 1, taken from the above-referenced co-owned US patent application, illustrates the froth flotation principle for the specific case of hydrophobic particles. These hydrophobic particles 200 come in contact with and adhere to bubbles 100 and rise with them to the surface to form a froth in which the particles can be easily skimmed from the solution 300, while hydrophilic particles remain as waste within the solution. FIG. 1 specifically shows nano-bubbles 100 which have been shown to increase efficiency of the flotation process. Various reactants and surfactants can be added to the solution to bias the bubbles' attachment towards or away from a given type of particle.
Froth flotation as well as flocculation are both conventional beneficiation processes for recovering valuable particles or contaminants. Particles such as ink or mineral present in the pulp typically have a very broad size distribution. For example, the size of ink particles have been reported to range from about 10 microns to 600 microns.
Fine particles with a diameter of less than 30 microns are documented to be particularly resistant to flotation. For this reason sometimes a coagulation or flocculation process is initiated in the pulp before flotation processes are used to separate the coagulated/flocculated particles. These methods typically use coagulants, flocculation and nano-bubbles to attach particles of sizes smaller than a few microns to each other to form a floc.
Numerous investigations have been performed on fine particles such as mineral, coal, ink and contaminants, reporting various physical and chemical separation techniques:    U.S. Pat. Nos. 5,068,031; 3,393,780; and 4,308,149 describe polymer flocculation.    Koh, P. T. L., and Warren, L. J., [Trans. Inst. Min. Metall., 86, C94-95; 1977] and also Song, S., and Trass, O., [Fuel, 76, 839-844, 1997] describe hydrophobic flocculation.    Van Kleef, R. P. A. R., Myron, H. W., Wyder, P., and Parker M. R., [IEEE Trans. On Magn. Mag-20, 1168-1170, 1984] describe magnetic flocculation.    U.S. Pat. No. 3,976,269 discusses polymeric flocculation that include micro-bubbles in the floc.    Zabel, T. F. [INNOVATIONS IN FLOTATION TECHNOLOGY, P. Mavros and K. A. Matis (eds), Kluwer Academic Publishers, p. 431-454, 1992] discusses micro-bubble flotation.    Iannicelli, J. [BENEFICIATION OF MINERAL FINES, P. Somasundaran and N. Arbiter (eds.), AIME, Inc., p. 363-380, 1979] and Wasmuth, H. D., and Unkelbach, K. H. [Minerals Engineering, 4, 825, 1991] respectively discuss high-gradient magnetic separation and super conducting separation.    Meadus, F. W. [The Canadian Mining and Metallurgical Bulletin, 61, 736, 1968] describes the development of oil/spherical agglomeration for fine coal cleaning.    U.S. Pat. No. 4,654,139 describes computer vision taking a plurality of images of the flocs in a basin.    U.S. Pat. No. 5,006,231 describes using optoelectric detectors with light emitting diodes to measure the solids concentration in the slurry so as to optimize the coagulations of materials.
What is needed in the art is a way to control the system for forming flocs.